In the early 1980's high-speed horizontal folding doors were introduced successfully into industrial and commercial use in Europe. The first such doors were installed in the United States in about 1985. These doors are typified by a horizontally folding door curtain, a header at the top of the door which supports the door suspension and contains an electrical, pneumatic or hydraulic actuating mechanism which causes the door curtain to rapidly fold to one or both of the outer edges or jambs of the door frame into a fan-fold position. The door curtain is attached to folding arms at the top of the door opening which are in turn suspended from a guide track attached to the header and connected to the actuating mechanism within the header. The door curtain itself may be in the form of panels of fabric or other sturdy, flexible material descending from the folding arms. Optimally, this descending curtain is made of a strong, clear, flexible plastic material which permits it to serve its function as a closure for the door opening while permitting the operators of vehicles and the like to see through the door for safety and traffic control purposes. Vertical hinge means at one or both sides or jambs of the door opening cooperate with the folding mechanism within the header of the door and retain the outermost edge of the door curtain within close proximity to the door jamb.
A pioneering example of such a door is found in German Pat. No. 3,048,763 to Klein.
These high-speed see-through doors have revolutionized the industrial door business. Because the doors are transparent, operators can see through them readily, insuring that safety is maintained. Such doors can be fast operating--a typical 35' door cycling opened and closed in 5 seconds or less. A typical 10' door of this type can cycle in 3 seconds or less.
Because the doors are able to operate so rapidly, as compared to previously available industrial sliding, rollup or swinging doors, they are particularly useful in situations where there is a sizable difference between the temperatures on either side of the door. A typical example would be a warehouse where such a high-speed, horizontal folding door may be utilized between an air-conditioned working structure and an outside loading dock. The door, in such a case, would be fitted with an automatic control in the form of an electric eye beam, pressure tredle or the like which would actuate the door when triggered by a forklift or other vehicle. The door would open rapidly, the forklift would go through actuating a closing control circuit, and the door would swiftly close behind, thereby minimizing the amount of time the door was open and helping to preserve the air-conditioned environment on the inside of the building. No other type of previously known industrial or commercial door is as effective as the high speed, horizontal folding door for such installations.
Another advantage of high-speed, horizontal folding doors is that they may be manufactured easily in a variety of large sizes up to about 50' wide and 28' high and are thus suitable for a wide variety of industrial and commercial applications.
Industrial doors comprising a series of adjacent flexible plastic strips suspended from a doorway are generally known in the prior art. See, for example, Catan U.S. Pat. No. 4,289,190 issued Sept. 15, 1981, Barbant U.S. Pat. No. 4,449,270 issued May 22, 1984, Schaefer U.S. Pat. No. 4,388,961 issued June 21, 1983, Romano U.S. Pat. No. 4,355,678 issued Oct. 26, 1982, Simon U.S. Pat. No. 4,335,777 issued June 22, 1982, and Sills U.K. Patent Application No. 2,080,379 published Feb. 3, 1982.
High-speed industrial folding doors of the type previously discussed include a door curtain in the form of a series of overlapping panels, strips or hinged sections which draw to one side in a fan-folded position. Typical suspension systems for such folding door curtains include a series of rack sections connected to each corresponding section of the curtain secured to suitable means for effecting a fan-fold opening and closing movement. Each rack section typically can be connected to an overhead guide track by a series of pins pivotally connected to rollers, as illustrated by Romano U.S. Pat. No. 4,083,395 issued Apr. 11, 1978. In lieu of rollers, simple sliding support devices can be employed, such as described in Sandall U.K. Patent Specification No. 1,554,159 published Oct. 17, 1979. The wheels or support devices are typically interlocked with the guide track. Comeau U.S. Pat. No. 4,274,467 issued June 23, 1981, illustrates such a fan-fold type drapery suspension system.
As described previously, high-speed, horizontal folding doors have proved highly useful, particularly in industrial situations where the environment on one side of the door is markedly different from the environment on the other side of the door. A further example of a situation of this sort which can provide very difficult operating conditions for such a door is a meat packing plant in which the plant building contains a freezer room in which meat is kept in a frozen condition. In such a situation the main part of the building might be at normal room temperature, say 60.degree. to 70.degree. F., while the freezer compartment would be at 30.degree. F. or less. Because of the large amount of money invested in energy for keeping such freezer rooms cold, in the past such rooms have been typically fitted with doors of one kind or another. The high-speed, horizontal folding door of the sort previously described is particularly suited to such an application and enables vehicles and workmen to pass in and out of the freezer compartment with a minimum door opening time and with good visibility.
In practice, in such an environment, a number of problems arise. For example, contact of warm, moisture laden air from the warm side of the door opening with the chilled components of the door causes frost and ice to form on the door components and the floor of the door opening.
In particular, frost or ice formation at four separate locations in horizontal folding door installations causes interference with the proper function of the door. These are:
(1) at the header and guide track where the door-actuating mechanism is located. If frost or ice forms sufficiently thickly on the header or guide track, it interferes with the movement of the folding arms, the seal members or the carriage of the door, thereby negatively affecting the operation of the door;
(2) at the side hinge pipe or pipes of the door where ice formation on the side jambs of the door causes interference with the hinge pipe on which the outermost panel of the door pivots, thereby affecting the overall operation of the door;
(3) on the material of the door itself. Since these doors are particularly effective when made out of a transparent material so that vehicle operators and others may see through door in advance of door opening, any formation of frost or ice obscuring vision through the door would defeat one of the principle purposes of such a door; and
(4) on the floor of the door opening. Frost and ice accumulation at this point is plainly a safety risk and must be controlled. Frost and ice accumulation on the floor of the door opening can also present operational difficulties. If frost and ice build up sufficiently, it can reach the lower edges of the transparent, flexible strips of the door curtain, abrading and damaging the edges. In some cases, frost on the floor is brushed toward the jambs of the door by the movement of the door curtain and eventually accumulates in the area of the jambs. Such accumulation interferes with the proper folding of the individual panels of the door curtain.
In the past, the art has made numerous attempts to deal with frost and ice formation in doors for various refrigerated structures. Numerous workers in the prior art have endeavored to use various heating devices to prevent frost formation around the sealing edges of conventional swinging doors as found on household refrigerators and freezers. See, for example, Knight U.S. Pat. No. 1,992,011 issued Feb. 19, 1935; Haggerty U.S. Pat. No. 2,420,240 issued May 6, 1947; Foster U.S. Pat. No. 2,493,125 issued Jan. 3, 1950; Southworth U.S. Pat. No. 2,809,402 issued Oct. 15, 1957; Taylor U.S. Pat. No. 3,135,100 issued June 2, 1964; Grubbs U.S. Pat. No. 2,731,804 issued Jan. 24, 1956; Rundell U.S. Pat. No. 3,254,503 issued June 7, 1966; Thomas U.S. Pat. No. 3,869,873 issued Mar. 11, 1975; Stowik U.S. Pat. No. 4,080,764 issued Mar. 28, 1978; Thaxter U.S. Pat. No. 2,238,511 issued Apr. 15, 1941; Barroero U.S. Pat. No. 2,858,408 issued Oct. 28, 1958; Barroero U.S. Pat. No. 3,449,925 issued June 17, 1969; Rifkin U.S. Pat. No. 2,460,469 issued Feb. 1, 1949; Miller U.S. Pat. No. 3,462,885 issued Aug. 26, 1969; McQueen U.S. Pat. No. 4,448,232 issued May 15, 1984; Gidge U.S. Pat. No. 4,313,485 issued Feb. 2, 1982 and Gidge U.S. Pat. No. 4,420,027 issued Dec. 13, 1983.
Workers in the prior art have also endeavored to devise various systems to prevent frost and ice interference with horizontal and vertical sliding doors, for example, in Thaxter U.S. Pat. No. 2,238,511 issued Apr. 15, 1941; Barroero U.S. Pat. No. 2,858,408 issued Oct. 28, 1958; Barroero U.S. Pat. No. 3,449,925 issued June 17, 1969.
The prior art has also endeavored to prevent frost formation at the sealing joints of refrigerated cases utilizing pull-out drawers, e.g., Rifkin U.S. Pat. No. 2,460,469 issued Feb. 1, 1949.
Rytec Corporation of Jackson, Wisconsin has marketed high-speed folding doors including flaccid heat wires in the header and jambs of the door for frost prevention. In these prior art doors the flaccid heat wires were retained in place by heat resistant tape. In practice it was found that such a structure was slow and expensive to manufacture and that the taped-in-place heat wires did not always stay in place in service resulting in non-uniform heating of the header or jamb and attendant service problems.
As is evident, the art has not successfully directed itself to the prevention of frost and ice formation in high-speed, horizontal folding doors or in the prevention of frost and ice formation which interferes with the actuating mechanism of a power operated door at low manufacturing cost and good in-service reliability.
Nor has the prior art directed its attention to the prevention of frost and ice formation on the clear curtain panels of a high-speed folding door, although transparent curtain doors have been used in environments where frost formation is likely to be a problem; e.g. Gidge U.S. Pat. No. 4,313,485 issued Feb. 2, 1982 and Gidge U.S. Pat. No. 4,420,027 issued Dec. 13, 1983.
The present invention substantially prevents frost and ice formation interfering with the action of a high-speed, power operated horizontal folding door and substantially prevents ice and frost formation on the transparent descending curtain of a folding door and on the floor of the door opening. The present invention does so with low utilization of energy; at relatively low manufacturing cost; with manufacturing ease and with in-service reliability.